my a/c clutch engages only when it's "cold" and when i rev hard. meaning that at idle, it usually doesn't engage.

thinking it was a weak a/c magnetic clutch, replaced it but the problem persists. connecting a wire directly from the batt to the clutch to test it affirmed that it simply wouldn't engage at the batt's voltage (and the batt is new).

i can only conclude that the pulley mechanism is faulty. any other areas i could examine?

the a/c uses a piston type compressor, not sure if that's what the "york" compressor refers to though...

appreciate it if someone could tell me the part number of the pulley, and if it is available seperately without the clutch. thanks!

The York compressors mounted on 115 and diesel motors were mounted in rubber. You undoubtably have a bad ground. Run a separate HEAVY ground wire from the compressor body to the intake manifold.

To verify the circuit electrically, an amp meter should show 2-4amps, with less than .1v drop at both the positive and negative connections (the negative connection on a york clutch coil is its mounting bolts). If I am right about the ground problem, there will be significant voltage (voltage drop) between the body of the compressor and any real ground.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Steve,

Have measured the voltage from the positive terminal of the clutch, to the negative terminal (mounting bolts), and using the intake manifold as a "real ground". Both yield about 12.9volts, with no significant differences. This is when the clutch is not engaged.

If I give it a tap or rev the engine hard to engage the clutch, the voltage will drop to just below 12volts, about 11.9volts.

Taking a reading between the mounting bolt and the intake manifold also verifies that there's no voltage difference.

Hence, what can I conclude? A mechanically faulty pulley?

BTW, what kind of current (amperes) does the clutch draw? Is there a difference using the compressor body or the clutch mounting bolts as ground?

Thanks.

Roland